Liquid crystalline medium

ABSTRACT

The present invention relates to a liquid-crystalline medium based on a mixture of polar compounds having negative dielectric anisotropy (Δ∈), which is distinguished by the fact that it has a value for the ratio γ 1 /Δn 2  in the range 6-45 with a clearing point of &gt;60° C. and a Δ∈ of ≦−2.3. Media of this type are particularly suitable for electro-optical displays having active-matrix addressing based on the ECB, PA LCD, FFS or IPS effect.

The present invention relates to a liquid-crystalline medium and to the use thereof in liquid-crystal displays, in particular liquid-crystal displays addressed by means of an active matrix (AMDs or AMLCDs for active matrix addressed liquid crystal displays). Particular preference is given to displays which use an active matrix comprising thin-film transistors (TFTs) or varistors. AMDs of this type can use various active electronic switching elements. The most widespread are displays which use three-pole switching elements. Examples of three-pole switching elements of this type are MOS (metal oxide silicon) transistors or the above-mentioned TFTs or varistors. Various semiconductor materials, predominantly silicon, or also cadmium selenide, are used in the TFTs. In particular, polycrystalline silicon or amorphous silicon is used. In contrast to the three-pole electronic switching elements, matrices of two-pole switching elements, such as, for example, MIM (metal insulator metal) diodes, ring diodes or back-to-back diodes, can also be employed in AMDs.

In liquid-crystal displays of this type, the liquid crystals are used as dielectrics whose optical properties change reversibly on application of an electrical voltage. Electro-optical displays which use liquid crystals as media are known to the person skilled in the art. These liquid-crystal displays use various electro-optical effects.

The most widespread conventional displays use the TN effect (twisted nematic, having a nematic structure twisted by about 90°), the STN effect (supertwisted nematic) or the SBE effect (supertwisted birefringence effect). In these and similar electro-optical effects, liquid-crystalline media having positive dielectric anisotropy (Δ∈) are used.

In contrast to the said conventional displays, which require liquid-crystal media having positive dielectric anisotropy, there are other electro-optical effects which use liquid-crystal media having negative dielectric anisotropy, such as, for example, the ECB effect (electrically controlled birefringence) and its subforms DAP (deformation of aligned phases), VAN (vertically aligned nematics), MVA (multidomain vertical alignment), ASV (advanced super view), PVA (patterned vertical alignment) and CSH (colour super homeotropics).

The principle of electrically controlled birefringence, the ECB effect (electrically controlled birefringence) or also DAP effect (deformation of aligned phases), was described for the first time in 1971 (M. F. Schieckel and K. Fahrenschon, “Deformation of nematic liquid crystals with vertical orientation in electrical fields”, Appl. Phys. Left. 19 (1971), 3912). This was followed by papers by J. F. Kahn (Appl. Phys. Lett. 20 (1972), 1193) and G. Labrunie and J. Robert (J. Appl. Phys. 44 (1973), 4869).

The papers by J. Robert and F. Clerc (SID 80 Digest Techn. Papers (1980), 30), J. Duchene (Displays 7 (1986), 3) and H. Schad (SID 82 Digest Techn. Papers (1982), 244) have shown that liquid-crystalline phases must have high values for the ratio of the elastic constants K₃/K₁, high values for the optical anisotropy Δn and values for the dielectric anisotropy Δ∈ of −0.5 to −5 in order to be usable for high-information display elements based on the ECB effect. Electro-optical display elements based on the ECB effect have a homeotropic edge alignment.

The IPS effect (in plane switching) increasingly employed recently can use both dielectrically positive and also dielectrically negative liquid-crystal media, similarly to “guest/host” displays, which can employ dyes, depending on the display mode used, either in dielectrically positive or in dielectrically negative media. A further highly promising type of liquid-crystal displays are so-called “axially symmetric microdomain” (ASM for short) displays, which are preferably addressed by means of plasma arrays (PA LCDs from “plasma addressed liquid crystal displays”).

The liquid-crystal media employed in the above-mentioned liquid-crystal displays and in all liquid-crystal displays utilising similar effects generally comprise liquid-crystal compounds having the corresponding dielectric anisotropy, i.e. comprising compounds having positive dielectric anisotropy in the case of dielectrically positive media and comprising compounds having negative dielectric anisotropy in the case of dielectrically negative media.

The liquid-crystal media of the prior art generally have relatively low birefringence values, relatively high operating voltages (the threshold voltages (V₀) are often relatively high, in some cases greater than 2.3 V) and relatively long response times, which are inadequate, in particular, for video-capable displays. Furthermore, they are usually unsuitable for high operating temperatures and/or have inadequate low-temperature stabilities (LTSs). Thus, for example, the nematic phases often only extend down to −20° C. and in some cases even only down to −10° C.

For the most part, the liquid-crystal media of the prior art have relatively unfavourable values for Δn, which are often significantly smaller than 0.11 and in some cases smaller than 0.10. However, such small Δn values are not particularly advantageous, for example, for VAN displays, since they require the use of cells having relatively large layer thicknesses, of 4 μm or more, and thus result in response times which are unacceptably long for many applications. Thus, a d·Δn of approximately 0.30 μm is employed in the case of an untwisted director alignment.

However, the use of cells having very small layer thicknesses frequently results in low production yields in the displays. For fast-switching displays, Δn values in the range from 0.075 to 0.15 are preferably desired. This applies both in the case of ECB displays and also in the case of IPS displays.

Since the response times of the prior art displays, as already mentioned above, are often too long, the viscosities of the liquid-crystal media must be improved and thus reduced. This applies, in particular, to the rotational viscosity γ₁ and very particularly to the value thereof at low temperatures. A reduction in the flow viscosity ν₂₀ generally results, in particular in the case of displays having a homeotropic edge alignment of the liquid crystals (for example in the case of ECB and VAN displays), in a very desired shortening of the response times.

For industrial use of this effect in electro-optical display elements, there is a requirement for LC phases which have to satisfy a multiplicity of requirements. Particularly important here are the chemical resistance to moisture, air and physical influences, such as heat, radiation in the infrared, visible and ultraviolet regions, and direct and alternating electric fields.

Furthermore, LC phases which can be used industrially are required to have a liquid-crystalline mesophase in a suitable temperature range and low viscosities.

None of the series of compounds having a liquid-crystalline mesophase that are known to date includes a single compound which meets all these requirements. In general, therefore, mixtures of from two to 25, preferably from three to 18, compounds are prepared in order to obtain substances which can be used as LC phases. However, it has not been possible to prepare optimum phases easily in this way, since no liquid-crystal materials having significantly negative dielectric anisotropy and adequate long-term stability were hitherto available.

The displays based on the ECB effect and optionally on the IPS or PALCD effect have to date required specific, complex matching of the liquid-crystal mixtures to be employed to the particular mode or the particular configuration, in particular concerning Δn and Δ∈ values and the rotational and flow viscosities.

Surprisingly, it has now been found that liquid-crystalline mixtures having negative anisotropy which have a certain ratio of γ₁ and Δn or the square thereof do not have the disadvantages of the media from the prior art, or at least only do so to a significantly reduced extent. The present mixture concept according to the invention enables negative mixtures which can be employed universally for the ECB effect to be conceived easily for the various modes. The mixtures according to the invention are particularly suitable for VAN displays in the MVA and PVA configurations, furthermore for IPS, FFS and PA LCD.

The present invention thus relates to a liquid-crystalline medium based on a mixture of polar compounds having negative dielectric anisotropy (Δ∈), which is distinguished by the fact that it has a value for the ratio γ₁/Δn² in the range 6-45 Pa·s with a clearing point of >60° C. and a Δ∈ of ≦−2.3.

All values for the ratio of γ₁/Δn² indicated in this application have the unit [Pa·s], unless stated otherwise.

The mixtures according to the invention are distinguished by their short response times in ECB displays, a broad nematic phase and relatively high values for the voltage holding ratio (HR). The mixtures according to the invention having a γ₁/Δn² ratio of this type furthermore exhibit very favourable values for the capacitive threshold and at the same time very good low-temperature stability.

The invention therefore also relates to the use of the liquid-crystalline mixtures, in particular for displays based on the ECB, PALCD and IPS effect, and to the corresponding displays containing the mixtures according to the invention.

Preferred embodiments of the mixture concept according to the invention are indicated below.

The mixtures according to the invention preferably have a γ₁/Δn² of 6-30, preferably of 6-22.

The values for the optical anisotropy Δn are preferably in the range 0.08-0.12. Particular preference is given to mixtures having a Δn=0.08±0.01, furthermore having a Δn=0.10±0.005 and Δn=0.12±0.01.

The mixtures according to the invention preferably have clearing points of ≧65° C., in particular of ≧69° C.

The thresholds V₀ (capacitive) are preferably in the range 1.8-2.3 V.

The temperature stability (LTS) is preferably at least 1000 h at temperatures of ≦−20° C., in particular ≦−30° C. and very particularly preferably ≦−40° C.

Mixtures which satisfy the required ratio of γ₁/Δn² preferably have, depending on Δn, Δ∈ and the clearing point, the following rotational viscosities, as tabulated below:

1. Clearing point 70° C.±5° C. and Δ∈ of −3.0±0.6

Δn Rotational viscosities γ₁ 0.08 ± 0.005 ≦125 mPa · s, preferably ≦105 mPa · s 0.09 ± 0.005 ≦130 mPa · s, preferably ≦105 mPa · s 0.10 ± 0.005 ≦135 mPa · s, preferably ≦110 mPa · s 0.11 ± 0.005 ≦145 mPa · s, preferably ≦120 mPa · s 0.12 ± 0.005 ≦150 mPa · s, preferably ≦125 mPa · s 0.13 ± 0.005 ≦160 mPa · s, preferably ≦135 mPa · s 0.15 ± 0.01 ≦170 mPa · s, preferably ≦145 mPa · s

-   -   The value for the ratio of γ₁/Δn² is preferably in the range         8.6-18.5. The thresholds are preferably <2.3 V, in particular in         the range 2.0-2.3 V.         2. Clearing point 70° C.±5° C. and Δ∈ of −4.0±0.4

Δn Rotational viscosities γ₁ 0.08 ± 0.005 ≦140 mPa · s, preferably ≦120 mPa · s 0.09 ± 0.005 ≦165 mPa · s, preferably ≦145 mPa · s 0.10 ± 0.005 ≦185 mPa · s, preferably ≦150 mPa · s 0.11 ± 0.005 ≦190 mPa · s, preferably ≦160 mPa · s 0.12 ± 0.005 ≦195 mPa · s, preferably ≦175 mPa · s 0.13 ± 0.005 ≦205 mPa · s, preferably ≦180 mPa · s 0.15 ± 0.01 ≦220 mPa · s, preferably ≦185 mPa · s

-   -   The value for the ratio of γ₁/Δn² is preferably in the range         9.5-20.0. The thresholds are preferably <2.1 V, in particular in         the range 1.8-2.1 V.         3. Clearing point 70° C.±5° C. and Δ∈ of −5.0±0.6

Δn Rotational viscosities γ₁ 0.08 ± 0.005 ≦185 mPa · s, preferably ≦175 mPa · s 0.09 ± 0.005 ≦200 mPa · s, preferably ≦165 mPa · s 0.10 ± 0.005 ≦210 mPa · s, preferably ≦165 mPa · s 0.11 ± 0.005 ≦220 mPa · s, preferably ≦190 mPa · s 0.12 ± 0.005 ≦230 mPa · s, preferably ≦200 mPa · s 0.13 ± 0.005 ≦250 mPa · s, preferably ≦210 mPa · s 0.15 ± 0.01  ≦270 mPa · s, preferably ≦220 mPa · s

-   -   The value for the ratio of γ₁/Δn² is preferably in the range         12.0-22.0. In the case of Δn values of 0.08±0.005, the value may         also be in the range 26-28. The thresholds are preferably <1.9         V, in particular in the range 1.7-1.8 V.         4. Clearing point 90° C.±5° C. and Δ∈ of −3.0±0.6

Δn Rotational viscosities γ₁ 0.08 ± 0.005 ≦160 mPa · s, preferably ≦130 mPa · s 0.09 ± 0.005 ≦170 mPa · s, preferably ≦135 mPa · s 0.10 ± 0.005 ≦180 mPa · s, preferably ≦140 mPa · s 0.11 ± 0.005 ≦190 mPa · s, preferably ≦150 mPa · s 0.12 ± 0.005 ≦200 mPa · s, preferably ≦190 mPa · s 0.13 ± 0.005 ≦210 mPa · s, preferably ≦195 mPa · s 0.15 ± 0.01  ≦220 mPa · s, preferably ≦200 mPa · s

-   -   The value for the ratio of γ₁/Δn² is preferably in the range         12.0-23.0. The thresholds are preferably <2.6 V, in particular         in the range 2.30-2.55 V.         5. Clearing point 90° C.±5° C. and Δ∈ of −4.0±0.4

Δn Rotational viscosities γ₁ 0.08 ± 0.005 ≦185 mPa · s, preferably ≦150 mPa · s 0.09 ± 0.005 ≦195 mPa · s, preferably ≦160 mPa · s 0.10 ± 0.005 ≦215 mPa · s, preferably ≦200 mPa · s 0.11 ± 0.005 ≦215 mPa · s, preferably ≦190 mPa · s 0.12 ± 0.005 ≦215 mPa · s, preferably ≦200 mPa · s 0.13 ± 0.005 ≦235 mPa · s, preferably ≦210 mPa · s 0.15 ± 0.01  ≦250 mPa · s, preferably ≦210 mPa · s

-   -   The value for the ratio of γ₁/Δn² is preferably in the range         14.5-22.0. The thresholds are preferably <2.25 V, in particular         in the range 2.00-2.25 V.         6. Clearing point 90° C.±5° C. and Δ∈ of −5.0±0.6

Δn Rotational viscosities γ₁ 0.08 ± 0.005 ≦280 mPa · s, preferably ≦265 mPa · s 0.09 ± 0.005 ≦275 mPa · s, preferably ≦260 mPa · s 0.10 ± 0.005 ≦275 mPa · s, preferably ≦260 mPa · s 0.11 ± 0.005 ≦275 mPa · s, preferably ≦265 mPa · s 0.12 ± 0.005 ≦280 mPa · s, preferably ≦265 mPa · s

-   -   The value for the ratio of γ₁/Δn² is preferably in the range         18.0-25.0. In the case of Δn values of 0.08±0.005, the value may         also be in the range 40-45. The thresholds are preferably <2.0         V, in particular in the range 1.8-2.0 V.

Mixtures according to the invention having clearing points of 75-85° C. each have γ₁/Δn² values and γ₁ values between the above-mentioned limits for 70±5° C. and 90±5° C.

Preferred embodiments of the mixtures according to the invention with respect to their composition are mentioned below:

-   a) Liquid-crystalline medium which comprises at least two compounds     of the formulae IA, IB and/or II

-   -   in which     -   R¹ and R² each, independently of one another, denote H, an alkyl         or alkenyl radical having up to 15 C atoms which is         unsubstituted, monosubstituted by CN or CF₃ or at least         monosubstituted by halogen, where, in addition, one or more CH₂         groups in these radicals may be replaced by —O—, —S—,

-   -    —C≡C—, —OCF₂—, —CF₂O—, —OC—O— or —O—CO— in such a way that O         atoms are not linked directly to one another, and     -   v denotes 1 to 6.     -   R¹ and R² preferably denote straight-chain alkyl or         straight-chain alkenyl.     -   Preferred mixtures, in particular having an n value of         0.08-0.09, comprise in total four compounds of the formulae

-   b) Liquid-crystalline medium which additionally comprises one or     more compounds of the formula III

-   -   in which     -   R³¹ and R³² each, independently of one another, denote a         straight-chain alkyl, alkylalkoxy or alkoxy radical having up to         12 C atoms, and

-   -   denotes

-   -    and     -   Z denotes a single bond, —C₂H₄—, —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—,         —O(CH₂)₃—, —CH═CHCH₂CH₂—, —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —CF₂O—,         —OCF₂—, —COO—, —OCO—, —C₂F₄—, —CHFCF₂—, —CF═CF—, —CH═CF—,         —CF═CH—, —CH₂—,     -   The mixtures according to the invention may comprise up to 50%         by weight of neutral compounds, preferably selected from the         compounds of the formula III.

-   c) Liquid-crystalline medium which comprises four, five, six or     more, preferably two or three, compounds of the formulae IA and/or     IB.

-   d) Liquid-crystalline medium in which R¹ and R² in the formulae IA     and IB preferably have the following meanings: straight-chain alkyl,     vinyl, 1E-alkenyl or 3-alkenyl.     -   If R¹ and/or R² denote alkenyl, it is preferably CH₂═CH,         CH₃—CH═CH, C₃H₇—CH═CH, CH₂═CH—C₂H₄ or CH₃—CH═CH—C₂H₄.     -   In the compounds IA, IB and II, v preferably denotes 2, 3 or 4.

-   e) Liquid-crystalline medium in which the proportion of compounds of     the formulae IA and/or IB in the mixture as a whole is at least 10%     by weight, preferably at least 25% by weight and very particularly     preferably ≧30% by weight.

-   f) Liquid-crystalline medium in which the proportion of compounds of     the formula II in the mixture as a whole is at least 10% by weight.

-   g) Liquid-crystalline medium comprising at least two, preferably     three, compounds of the formula II, in particular of the formula

-   -   R² preferably denotes ethyl, propyl or pentyl.

-   h) Liquid-crystalline medium in which the proportion of compounds of     the formula III in the mixture as a whole is at least 5% by weight.

-   i) Liquid-crystalline medium which additionally comprises a compound     selected from the formulae IIIa to IIIj:

-   -   in which     -   alkyl and alkyl* each, independently of one another, denote a         straight-chain alkyl radical having 1-6 C atoms, and     -   alkenyl and alkenyl* each, independently of one another, denote         a straight-chain alkenyl radical having 2-6 C atoms, preferably         vinyl, 1E-alkenyl or 3E-alkenyl.     -   The medium according to the invention preferably comprises at         least one compound of the formula IIIa, formula IIIb and/or         formula IIIe, preferably in amounts of >5% by weight, in         particular >10% by weight, very particularly preferably >20% by         weight.     -   Particularly preferred compounds of the formulae IIIe and IIIf         are mentioned below:

-   j) Liquid-crystalline medium which comprises at least three     compounds of the formula IIIe, preferably selected from the group of     the compounds

-   -   The proportion of the compounds IIIe-1, IIIe-2 and/or IIIe-3 in         the mixture, preferably having a Δn=0.08 (±0.005), is preferably         ≧20% by weight, in particular ≧30% by weight. alkyl preferably         denotes C_(n)H_(2n+1), where n=3, 4 or 5.     -   Preference is furthermore given to media which comprise the         compound of the formula

-   -   preferably in concentrations >20% by weight, in particular >30%         by weight, preferably in combination with the compound of the         formula

-   -   The latter compounds are preferably present in the mixture in         amounts of 5-40% by weight.

-   k) Liquid-crystalline medium which essentially consists of:     -   10-40% by weight of one or more compounds of the formulae IA and         IB, and     -   10-40% by weight of one or more compounds of the formula II.

-   l) Liquid-crystalline medium which additionally comprises one or     more tetracyclic compounds of the formulae

-   -   in which     -   R⁷ and R⁸ each, independently of one another, have one of the         meanings indicated for R¹ in Claim 1, and     -   w and x each, independently of one another, denote 1 to 6.

-   m) Particularly preferred media comprise one or more indane     compounds selected from the group of the compounds of the formulae     In-a to In-d:

-   -   in which     -   alkyl and alkyl* each, independently of one another, denote a         straight-chain alkyl radical having 1-6 C atoms, and     -   alkenyl denotes a straight-chain alkenyl radical having 2-6 C         atoms,     -   alkyl* preferably denotes CH₃, C₂H₅ or n-C₃H₇.     -   The mixtures according to the invention preferably comprise a         compound of the formula In-a or In-b, in particular a compound         of the formula In-a. The proportion of the indane compounds in         the mixture as a whole is at least 5% by weight, preferably at         least 10% by weight.     -   n) Liquid-crystalline medium which additionally comprises one or         more compounds of the formulae

-   -   in which R¹³-R²⁷ each, independently of one another, have the         meanings indicated for R¹, and z and m each, independently of         one another, denote 1-6. R^(E) denotes H, CH₃, C₂H₅ or n-C₃H₇,         and x denotes 0, 1, 2 or 3.     -   The said compounds are preferably each present in the mixture as         a whole in amounts of at least 5% by weight.     -   Mixtures having a Δn in the range 0.08-0.12 preferably comprise         compounds of the formula

-   -   in concentrations of ≧5% by weight, preferably ≧10% by weight.     -   Mixtures of this type furthermore comprise compounds of the         formula II in amounts of ≧2% by weight.     -   The compounds of the formula

-   -   are particularly suitable for mixtures having a Δn value in the         range 0.07-0.10, in particular 0.07-0.09. These compounds, in         which R²⁷ preferably denotes alkyl, are preferably employed in         concentrations of 5-20% by weight.

-   o) Liquid-crystalline medium additionally comprising one or more     fluorinated terphenyls of the formulae T-1 to T-22

-   -   in which     -   R has the meanings indicated for R¹.     -   R is preferably straight-chain alkyl, alkoxy or alkylalkoxy,         each having 1-6 C atoms, alkenyl or alkenyloxy having 2-6 C         atoms. R preferably denotes methyl, ethyl, propyl, butyl,         pentyl, hexyl, methoxy, ethoxy, propoxy, butoxy, pentoxy.     -   The medium according to the invention preferably comprises the         terphenyls of the formulae T-1 to T-22 in amounts of 2-30% by         weight, in particular of 5-20% by weight.     -   Particular preference is given to compounds of the formulae T-1,         T-2, T-3 and T-22. In these compounds, R preferably denotes         alkyl, furthermore alkoxy, each having 1-5 C atoms.     -   The terphenyls are preferably employed in mixtures having a         Δn≧0.10 in combination with the compounds of the formulae IA, IB         and II. Preferred mixtures comprise 2-20% by weight of         terphenyls and 5-30% by weight of the compounds of the formula

-   p) Liquid-crystalline medium additionally comprising one or more     biphenyls of the formulae B-1 to B-4

-   -   in which alkyl, alkyl*, alkenyl and alkenyl* have the         above-mentioned meanings.     -   The proportion of the biphenyls of the formulae B-1 to B-4 in         the mixture as a whole is preferably at least 3% by weight, in         particular ≧5% by weight.     -   Of the compounds of the formulae B-1 to B-4, the compounds of         the formulae B-1 and B-4 are particularly preferred.     -   Preferred biphenyls are likewise

-   q) Liquid-crystalline medium additionally comprising one or more     esters of the formulae E-1 to E-3

-   -   in which alkyl and alkyl* have the above-mentioned meanings.     -   The proportion of the esters in the mixture as a whole is         preferably at least 10% by weight, in particular ≧30% by weight.     -   Of the compounds E-1 to E-3, the compound E-1 is particularly         preferred.

-   r) Liquid-crystalline medium additionally comprising one or more     tolans of the formulae To-1 and To-2

-   -   in which R and alkyl have the above-mentioned meanings.     -   The proportion of the tolans To-1 and/or To-2 in the mixture as         a whole is preferably at least 5% by weight, in particular ≧20%         by weight.     -   In the compounds To-1 and To-2, R preferably denotes         straight-chain alkyl or alkoxy.

-   s) Liquid-crystalline medium additionally comprising one or more     nitriles of the formulae N-1 and N-2

-   -   in which R and alkyl have the above-mentioned meanings.     -   The proportion of the nitriles in the mixture as a whole is         preferably at least 5% by weight, in particular ≧25% by weight.

-   t) Liquid-crystalline medium comprising at least 10% by weight,     preferably ≧15% by weight, in particular ≧20% by weight, of     compounds of the formula B-4. Compounds of this type are preferably     used in mixtures having a Δn≧0.12. The biphenyls of the formula B-4     are preferably employed in combination with compounds of the     formulae II and/or B-1.     -   Preferred mixtures having a Δn≧0.12 comprise at least 15% by         weight of compounds of the formula II and/or ≧5% by weight of         compounds of the formula B-1 besides the compounds of the         formula B-4.     -   Compounds of the formula B-4 are furthermore preferably employed         in combination with terphenyls, preferably with T-1, T-2 and/or         T-3.

-   u) Liquid-crystalline medium comprising at least one compound of the     formulae Z-1 to Z-10

-   -   in which R and alkyl have the above-mentioned meanings, and p is         1 or 2,     -   preferably in amounts of ≧5% by weight, in particular ≧10% by         weight.     -   Particular preference is given to media which comprise one, two         or more compounds of the formulae Z-1 to Z-7 and additionally         one, two or more compounds of the formula II. Mixtures of this         type preferably comprise ≧10% by weight of compounds of the         formula II and optionally also compounds of the formula IA.

-   v) Liquid-crystalline medium comprising at least one compound of the     formula

-   -   Preferred compounds of the formula IB-M are the compounds IB-M1         to IB-M3:

-   -   The mixtures according to the invention preferably comprise at         least one compound of the formula IB-M, in particular the         compound IB-M1, IB-M2 and/or IB-M3, and at least one compound

-   w) Liquid-crystalline medium comprising at least one compound of the     formulae

-   -   preferably in amounts of 5-20% by weight, in particular in         combination with one or more compounds of the formulae T-1 to         T-21.

-   x) Liquid-crystalline medium comprising at least one compound of the     formula T-1 and at least one compound of the formula T-4.

-   y) Liquid-crystalline medium comprising at least one compound of the     formula

-   -   and at least one compound of the formula

The invention furthermore relates to an electro-optical display having active-matrix addressing based on the ECB effect, characterised in that it contains, as dielectric, a liquid-crystalline medium according to one of Claims 1 to 17.

The liquid-crystal mixture preferably has a nematic phase range of at least 60 K and a flow viscosity ν₂₀ of at most 30 mm²·s⁻¹, preferably <25 mm²·s⁻¹, at 20° C.

The liquid-crystal mixture according to the invention has a Δ∈ of about −2.3 to −8.0, in particular about −3.0 to −6.0, very particularly preferably ≦3.0 to −5.0.

The rotational viscosity γ₁ is preferably <200 mPa·s, in particular <190 mPa·s.

-   z) Liquid-crystalline medium comprising at least one compound of the     formulae O-1 to O-11

-   -   in which R¹ and R² have the above-mentioned meanings, R¹ and R²         preferably each, independently of one another, denote         straight-chain alkyl, furthermore alkenyl.     -   Preferred liquid-crystalline media according to the invention         comprise one or more substances having a Δ∈<2.3 which contain a         tetrahydronaphthyl or naphthyl unit, such as, for example, the         compounds of the formulae N-1 to N-5

-   -   in which R¹ and R² each, independently of one another, have the         above-mentioned meanings, preferably denote straight-chain         alkyl, straight-chain alkoxy or straight-chain alkenyl, and Z,         Z¹ and Z² each, independently of one another, denote —C₂H₄—,         —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CHCH₂CH₂—,         —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF—,         —CF═CH—, —CH═CF—, —CH₂— or a single bond.

The birefringence Δn in the liquid-crystal mixture is, generally, between 0.07 and 0.16, preferably between 0.08 and 0.12.

The mixtures according to the invention are suitable for all VA-TFT applications, such as, for example, VAN, MVA, (S)-PVA, ASV. They are furthermore suitable for IPS (in plane switching) and FFS (fringe field switching) LCD applications having negative Δ∈.

The individual components of the formulae IA, IB, II and III of the liquid-crystal phases according to the invention are either known or their preparation methods can readily be derived from the prior art by the relevant person skilled in the art since they are based on standard methods described in the literature.

The nematic liquid-crystal mixtures in the displays according to the invention generally comprise two components A and B, which themselves consist of one or more individual compounds.

Component A has clearly negative dielectric anisotropy and provides the nematic phase with a dielectric anisotropy of ≦−2.3. It preferably comprises compounds of the formulae IA and/or IB and II.

The proportion of component A is preferably between 45 and 100%, in particular between 60 and 100%.

For component A, one (or more) individual compound(s) having a value of Δ∈≦−0.8 is (are) preferably selected. This value must be more negative the smaller the proportion of A in the mixture as a whole.

Component B has pronounced nematogeneity and a flow viscosity of not greater than 30 mm²'s⁻¹, preferably not greater than 25 mm²'s⁻¹, at 20° C.

Particularly preferred individual compounds of component B are extremely low-viscosity nematic liquid crystals having a flow viscosity of not greater than 18, preferably not greater than 12 mm²·s⁻¹, at 20° C. Component B is monotropically or enantiotropically nematic, has no smectic phases and can prevent the occurrence of smectic phases in liquid-crystal mixtures down to very low temperatures. If, for example, various materials having high nematogeneity are each added to a smectic liquid-crystal mixture, the nematogeneity of these materials can be compared through the degree of suppression of smectic phases that is achieved. A multiplicity of suitable materials is known to the person skilled in the art from the literature. Particular preference is given to compounds of the formula III, furthermore compounds of the formulae B-1 to B-4, O-1 and O-2.

In addition, these liquid-crystal phases may also comprise more than 18 components, preferably 18 to 25 components.

The phases preferably comprise 4 to 15, in particular 5 to 12, compounds of the formulae IA and/or IB, II and optionally III.

Besides compounds of the formulae IA and/or IB, II and III, other constituents may also be present, for example in an amount of up to 45% of the mixture as a whole, but preferably up to 35%, in particular up to 10%.

The other constituents are preferably selected from nematic or nematogenic substances, in particular known substances, from the classes of the azoxybenzenes, benzylideneanilines, biphenyls, terphenyls, phenyl or cyclohexyl benzoates, phenyl or cyclohexyl cyclohexanecarboxylates, phenylcyclohexanes, cyclohexylbiphenyls, cyclohexylcyclohexanes, cyclehexylnaphthalenes, 1,4-biscyclohexylbiphenyls or cyclohexylpyrimidines, phenyl- or cyclohexyldioxanes, optionally halogenated stilbenes, benzyl phenyl ethers, tolans and substituted cinnamic acids.

The most important compounds which are suitable as constituents of liquid-crystal phases of this type can be characterised by the formula IV

R⁹-L-G-E-R¹⁰  IV

in which L and E each denote a carbocyclic or heterocyclic ring system from the group formed by 1,4-disubstituted benzene and cyclohexane rings, 4,4′-disubstituted biphenyl, phenylcyclohexane and cyclohexylcyclohexane systems, 2,5-disubstituted pyrimidine and 1,3-dioxane rings, 2,0-disubstituted naphthalene, di- and tetrahydronaphthalene, quinazoline and tetrahydroquinazoline, G denotes

-   -   —CH═CH— —N(O)═N—     -   —CH—CQ- —CH═N(O)—     -   —C≡C— —CH₂—CH₂—     -   —CO—O— —CH₂—O—     -   —CO—S— —CH₂—S—     -   —CH═N— —COO-Phe-COO—     -   —CF₂O— —CF═CF—     -   —OCF₂ —OCH₂—     -   —(CH₂)₄— —(CH₂)₃O         or a C—C single bond, Q denotes halogen, preferably chlorine, or         —CN, and R⁹ and R¹⁰ each denote alkyl, alkenyl, alkoxy,         alkanoyloxy or alkoxycarbonyloxy having up to 18, preferably up         to 8, carbon atoms, or one of these radicals alternatively         denotes CN, NC, NO₂, NCS, SCN, CF₃, OCF₃, F, Cl or Br.

In most of these compounds, R⁹ and R¹⁰ are different from one another, one of these radicals usually being an alkyl or alkoxy group. Other variants of the proposed substituents are also common. Many such substances or also mixtures thereof are commercially available. All these substances can be prepared by methods known from the literature.

It goes without saying for the person skilled in the art that the VA, IPS, FFS or PA LCD mixture according to the invention may also comprise compounds in which, for example, H, N, O, Cl and F have been replaced by the corresponding isotopes.

The construction of the liquid-crystal displays according to the invention corresponds to the usual geometry, as described, for example, in EP-A 0 240 379.

Besides the compounds of the formulae IA, IB, II and III, the mixtures according to the invention preferably comprise one or more of the compounds mentioned above.

The following abbreviations are used:

(n, m=1-6; z=1-6)

The liquid-crystal mixtures which can be used in accordance with the invention are prepared in a manner conventional per se. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. It is also possible to mix solutions of the components in an organic solvent, for example in acetone, chloroform or methanol, and to remove the solvent again, for example by distillation, after thorough mixing.

In the present application, the term dielectrically positive compounds denotes compounds having a Δ∈>1.5, the term dielectrically neutral compounds denotes those having −1.5≦Δ∈≦1.5 and the term dielectrically negative compounds denotes those having Δ∈<−1.5. The dielectric anisotropy of the compounds is determined here by dissolving 10% of the compounds in a liquid-crystalline host and determining the capacitance of this mixture in at least one test cell in each case having a layer thickness of 20 μm with a homeotropic and with a homogeneous surface alignment at 1 kHz. The measurement voltage is typically 0.5 V to 1.0 V, but is always lower than the capacitive threshold of the respective liquid-crystal mixture.

The host mixture used for dielectrically positive and dielectrically neutral compounds is ZLI-4792 and that used for dielectrically negative compounds is ZLI-2857, both from Merck KGaA, Germany. The values for the respective compounds to be investigated are obtained from the change in the dielectric constants of the host mixture after addition of the compound to be investigated and extrapolation to 100% of the compound employed.

The term threshold voltage relates in a conventional manner to the optical threshold for 10% relative contrast (V₁₀), unless explicitly stated otherwise.

In the present application, however, the term threshold voltage is used for the capacitive threshold voltage (V_(o)), also known as the Freedericks threshold, in relation to the liquid-crystal mixtures having negative dielectric anisotropy, unless explicitly stated otherwise.

All concentrations in this application, unless explicitly noted otherwise, are indicated in percent by weight and relate to the corresponding mixture or mixture component. All physical properties are determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and apply for a temperature of 20° C., unless explicitly stated otherwise. Δn is determined at 589 nm and Δ∈ at 1 kHz.

For the liquid-crystal media having negative dielectric anisotropy, the threshold voltage is determined as the capacitive threshold V₀ (also known as the Freedericks threshold) in test cells produced at Merck KGaA, Germany, with liquid crystal homeotropically aligned by alignment layer SE 1211 from Nissan Chemicals.

The dielectrics may also comprise further additives known to the person skilled in the art and described in the literature, such as, for example, UV absorbers, antioxidants, free-radical scavengers. For example, 0-15% of pleochroic dyes may be added, furthermore conductive salts, preferably ethyldimethyldodecylammonium 4-hexyloxybenzoate, tetrabutylammonium tetraphenylborate or complex salts of crown ethers (cf., for example, Haller et al., Mol. Cryst. Liq. Cryst. Volume 24, pages 249-258 (1973)), may be added in order to improve the conductivity or substances may be added in order to modify the dielectric anisotropy, the viscosity and/or the alignment of the nematic phases. Substances of this type are described, for example, in DE-A 22 09 127, 22 40 864, 23 21 632, 23 38 281, 24 50 088, 26 37 430 and 28 53 728.

The liquid-crystal media according to the invention may, if necessary, also comprise chiral dopants in the conventional amounts. The amount of these dopants employed is in total 0 to 10%, based on the amount of the mixture as a whole, preferably 0.1 to 6%. The concentration of the individual compounds employed is preferably 0.1 to 3%. The concentration of these and similar additives is not taken into account when indicating the concentrations and the concentration ranges of the liquid-crystal compounds in the liquid-crystal media.

Table A indicates possible dopants which can be added to the mixtures according to the invention.

TABLE A

  C 15

  CB 15

  CM 21

  R/S-811

  CM 44

  CM 45

  CM 47

  CN

  R/S-1011

  R/S-2011

  R/S-3011

  R/S-4011

  R/S-5011

Stabilisers which can be added, for example, to the mixtures according to the invention in amounts of 0-10% are mentioned below in Table B.

TABLE B

(n = 1-12)

The compositions consist of a plurality of compounds, preferably of 3 to 30, particularly preferably of 6 to 20 and very particularly preferably of 10 to 16 compounds, which are mixed in a conventional manner. In general, the desired amount of the components used in lesser amount is dissolved in the components making up the principal constituent, advantageously at elevated temperature. If the selected temperature is above the clearing point of the principal constituent, the completion of the dissolution process is particularly easy to observe. However, it is also possible to prepare the liquid-crystal mixtures by other conventional methods, for example using premixes or from a so-called “multibottle system”.

By means of suitable additives, the liquid-crystal phases according to the invention can be modified in such a way that they can be employed in any type of ECB, VAN, IPS, GH or ASM-PA LCD display known to date.

The following examples serve to illustrate the invention without restricting it. In the examples, the melting point T (C,N), the transition from the smectic (S) to the nematic (N) phase T (S,N) and clearing point T (N,I) of a liquid-crystal substance are indicated in degrees Celsius.

Furthermore:

V_(o) denotes the threshold voltage, capacitive [V] at 20° C. Δn denotes the optical anisotropy, measured at 20° C. and 589 nm Δ∈ denotes the dielectric anisotropy at 20° C. and 1 kHz cp. denotes clearing point [′C] γ₁ denotes rotational viscosity, measured at 20° C. [mPa·s] LTS denotes low-temperature stability, determined in test cells HR (20) denotes voltage holding ratio at 20° C. [%] HR (100) denotes voltage holding ratio after 5 min at 100° C. [%] HR (UV) denotes voltage holding ratio after UV exposure [%]

In order to measure the voltage holding ratio, cells with an Al-3046 alignment layer are used.

The display for measurement of the threshold voltage has two plane-parallel outer plates at a separation of 20 μm and electrode layers with overlying SE-1211 (Nissan Chemicals) alignment layers on the insides of the outer plates, which effect a homeotropic alignment of the liquid crystals.

USE EXAMPLES Example M1

CY-3-O4 16.00% Clearing point [° C.]: 71.0 CY-5-O2 13.00% Δn [589 nm, 20° C.]: 0.0822 CCY-3-O2 14.00% ε_(||) [kHz, 20° C.]: 3.6 CCY-2-1 13.00% Δε [kHz, 20° C.]: −3.3 CCY-3-1 10.00% K₁ [pN, 20° C.]: 13.3 CCH-35 10.00% K₃ [pN, 20° C.]: 14.0 CCH-303 5.00% γ₁ [mPa · s, 20° C.]: 125 CCH-301 12.00% V₀ [V]: 2.16 BCH-32 7.00% LTS: nematic >1000 h at −30° C. LTS: nematic >350 h at −40° C. HR (100): 93.0%

Example M2

CY-3-O4 18.00% Clearing point [° C.]: 70.5 CY-5-O4 14.00% Δn [589 nm, 20° C.]: 0.0825 CCY-3-O2 5.00% ε_(||) [kHz, 20° C.]: 3.4 CCY-5-O2 8.00% Δε [kHz, 20° C.]: −3.1 CPY-2-O2 3.00% K₁ [pN, 20° C.]: 14.0 CPY-3-O2 10.00% K₃ [pN, 20° C.]: 14.4 CC-3-V1 12.00% γ₁ [mPa · s, 20° C.]: 102 CC-5-V 15.00% V₀ [V]: 2.27 CC-3-2V 10.00% LTS: nematic >1000 h at CCH-35 5.00% −40° C. HR (100): 94.5%

Example M3

CY-3-O4 15.00% Clearing point [° C.]: 70.5 CY-5-O5 15.00% Δn [589 nm, 20° C.]: 0.0952 CCY-3-O2 10.00% ε_(||) [kHz, 20° C.]: 3.5 CCY-3-1 10.00% Δε [kHz, 20° C.]: −3.1 PCH-302 6.00% K₁ [pN, 20° C.]: 13.9 CC-5-V 6.00% K₃ [pN, 20° C.]: 14.6 CC-3-V1 12.00% γ₁ [mPa · s, 20° C.]: 133 CCH-35 5.00% V₀ [V]: 2.28 CPY-2-1 7.00% LTS: nematic >1000 h at CPY-3-1 7.00% −30° C. CPY-5-1 7.00%

Example M4

CY-3-O4 14.00% Clearing point [° C.]: 69.5 CY-5-O2 8.00% Δn [589 nm, 20° C.]: 0.1005 CY-5-O4 15.00% ε_(||) [kHz, 20° C.]: 3.6 BCH-32 8.00% Δε [kHz, 20° C.]: −3.3 CCP-V2-1 7.00% K₁ [pN, 20° C.]: 12.5 CC-3-V1 8.00% K₃ [pN, 20° C.]: 13.5 CC-3-V 18.00% γ₁ [mPa · s, 20° C.]: 106 CPY-2-O2 10.00% V₀ [V]: 2.14 CPY-3-O2 12.00% LTS: nematic >1000 h at −40° C.

Example M5

CY-3-O4 15.00% Clearing point [° C.]: 73.5 CY-5-O4 13.00% Δn [589 nm, 20° C.]: 0.1198 PCH-53 5.00% ε_(||) [kHz, 20° C.]: 3.7 CCP-V-1 6.00% Δε [kHz, 20° C.]: −3.3 BCH-32 8.00% K₁ [pN, 20° C.]: 11.9 CC-3-V1 8.00% K₃ [pN, 20° C.]: 12.0 CC-5-V 9.00% γ₁ [mPa · s, 20° C.]: 150 CPY-2-O2 12.00% V₀ [V]: 2.01 CPY-3-O2 12.00% YPY-4-1 6.00% YPY-4-4 6.00%

Example M6

CY-3-O4 11.00% Clearing point [° C.]: 71.0 CY-5-O2 11.00% Δn [589 nm, 20° C.]: 0.1202 CPY-2-O2 12.00% ε_(||) [kHz, 20° C.]: 3.7 CPY-3-O2 9.00% Δε [kHz, 20° C.]: −3.0 BCH-32 9.00% K₁ [20° C.]: 12.4 CCH-301 12.00% K₃ [20° C.]: 11.7 CCH-303 12.00% γ₁ [mPa · s, 20° C.]: 125 CCH-35 6.00% V₀ [V]: 2.10 PYP-2-3 6.00% LTS: nematic >1000 h at PYP-2-4 12.00% −30° C.

Example M7

CY-3-O4 20.00% Clearing point [° C.]: 70.0 CY-5-O4 5.00% Δn [589 nm, 20° C.]: 0.1201 CPY-2-O2 12.00% ε_(||) [kHz, 20° C.]: 3.6 CPY-3-O2 12.00% Δε [kHz, 20° C.]: −3.2 PYP-2-3 10.00% K₁ [20° C.]: 11.7 PYP-2-4 10.00% K₃ [20° C.]: 12.4 CC-3-V1 12.00% γ₁ [mPa · s, 20° C.]: 116 CC-4-V 14.00% V₀ [V]: 2.09 CCH-34 5.00%

Example M8

BCH-32 10.00% Clearing point [° C.]: 72.0 CCP-V-1 10.00% Δn [589 nm, 20° C.]: 0.1512 CC-3-V1 12.00% ε_(||) [kHz, 20° C.]: 3.7 CPY-2-O2 12.00% Δε [kHz, 20° C.]: −3.6 CPY-3-O2 13.00% K₁ [20° C.]: 15.0 B-302FF 19.00% K₃ [20° C.]: 15.5 B-502FF 17.00% γ₁ [mPa · s, 20° C.]: 143 PP-1-4 7.00% V₀ [V]: 2.20 LTS: nematic >1000 h at −30° C.

Example M9

CY-3-O2 18.00% Clearing point [° C.]: 71.0 CY-3-O4 5.00% Δn [589 nm, 20° C.]: 0.0821 CY-5-O2 12.00% ε_(||) [kHz, 20° C.]: 3.7 CCY-3-O2 12.00% Δε [kHz, 20° C.]: −3.9 CCY-5-O2 3.00% K₁ [20° C.]: 13.1 CCY-2-1 4.00% K₃ [20° C.]: 14.9 CCY-3-1 8.00% γ₁ [mPa · s, 20° C.]: 130 CPY-3-O2 3.00% V₀ [V]: 2.07 CCH-35 5.00% LTS: nematic >1000 h at PCH-302 8.00% −40° C. CH-33 3.00% HR (100° C.): 93% CH-43 4.00% CC-5-V 15.00%

Example M10

CY-3-O4 9.00% Clearing point [° C.]: 69.0 CY-5-O2 14.00% Δn[589 nm, 20° C.]: 0.0813 CY-5-O4 16.00% ε_(||) [kHz, 20° C.]: 3.7 CCY-3-O2 11.00% Δε [kHz, 20° C.]: −4.2 CCH-35 6.00% K₁ [20° C.]: 13.1 CC-3-V1 7.00% K₃ [20° C.]: 14.1 CC-5-V 18.00% γ₁ [mPa · s, 20° C.]: 116 CPY-3-O2 4.00% V₀ [V]: 1.94 CCY-V-O2 15.00% LTS: nematic >1000 h at −30° C. LTS: nematic >600 h at −40° C. HR (100° C.): 94%

Example M11

CY-3-O4 17.00% Clearing point [° C.]: 70.5 CY-5-O2 9.00% Δn [589 nm, 20° C.]: 0.0993 CY-5-O4 14.00% ε_(||) [kHz, 20° C.]: 4.0 CPY-2-O2 7.00% Δε [kHz, 20° C.]: −4.2 CPY-3-O2 7.00% K₁ [20° C.]: 11.5 CCP-V-1 12.00% K₃ [20° C.]: 14.3 CCH-35 5.00% γ₁ [mPa · s, 20° C.]: 187 CC-3-V1 9.00% V₀ [V]: 1.95 CPQIY-3-O4 10.00% LTS: nematic >1000 h at CPQIY-5-O4 10.00% −30° C.

Example M12

CC-5-V 11.00% Clearing point [° C.]: 73.0 PCH-53 13.00% Δn [589 nm, 20° C.]: 0.0985 CY-3-O4 12.00% ε_(∥) [kHz, 20° C.]: 3.7 CY-5-O4 12.00% Δε [kHz, 20° C.]: −4.0 CCY-2-O2 12.00% K₁ [20° C.]: 13.8 CCY-3-O2 12.00% K₃ [20° C.]: 14.2 CCY-5-O2 8.00% γ₁ [mPa · s, 20° C.]: 163 CCY-2-1 10.00% V₀ [V]: 1.98 PYP-2-3 10.00%

Example M13

CY-3-O4 16.00% Clearing point [° C.]: 71.0 CY-5-O4 15.00% Δn [589 nm, 20° C.]: 0.1014 CY-5-O2 8.00% ε_(∥) [kHz, 20° C.]: 3.8 CCY-3-O2 6.00% Δε [kHz, 20° C.]: −4.0 BCH-32 7.00% K₁ [20° C.]: 13.9 CCH-35 5.00% K₃ [20° C.]: 13.0 CC-3-2V 10.00% γ₁ [mPa · s, 20° C.]: 141 CC-5-V 9.00% V₀ [V]: 1.89 CPY-2-O2 12.00% LTS: nematic >1000 h CPY-3-O2 12.00% at −30° C.

Example M14

CY-3-O4 20.00% Clearing point [° C.]: 73.5 CY-5-O2 9.00% Δn [589 nm, 20° C.]: 0.1202 CY-5-O4 4.00% ε_(∥) [kHz, 20° C.]: 3.7 BCH-32 10.00% Δε [kHz, 20° C.]: −3.8 PGIGI-3-F 2.00% K₁ [20° C.]: 13.0 CC-3-V1 11.00% K₃ [20° C.]: 13.1 CC-5-V 10.00% γ₁ [mPa · s, 20° C.]: 153 CPY-2-O2 14.00% V₀ [V]: 1.95 CPY-3-O2 12.00% LTS: nematic >1000 h YPY-4-1 2.00% at −20° C. YPY-4-4 2.00% YPY-5-5 2.00% YPY-4-2V 2.00%

Example M15

CY-3-O4 16.00% Clearing point [° C.]: 69.0 CY-5-O2 8.00% Δn [589 nm, 20° C.]: 0.1249 CY-5-O4 16.00% ε_(∥) [kHz, 20° C.]: 3.9 BCH-32 8.00% Δε [kHz, 20° C.]: −4.1 CC-5-V 8.00% K₁ [20° C.]: 12.7 CC-3-V1 8.00% K₃ [20° C.]: 13.1 CPY-2-O2 11.00% γ₁ [mPa · s, 20° C.]: 153 CPY-3-O2 11.00% V₀ [V]: 1.89 PYP-2-3 14.00% LTS: nematic >1000 h at −40° C.

Example M16

CY-3-O4 20.00% Clearing point [° C.]: 71.0 CY-5-O2 8.00% Δn [589 nm, 20° C.]: 0.1210 CY-5-O4 12.00% ε_(∥) [kHz, 20° C.]: 4.0 BCH-32 9.00% Δε [kHz, 20° C.]: −4.1 CCP-V-1 7.00% K₁ [20° C.]: 12.4 PGIGI-3-F 7.00% K₃ [20° C.]: 13.8 CC-3-V1 8.00% γ₁ [mPa · s, 20° C.]: 171 PCH-53 3.00% V₀ [V]: 1.94 CPY-2-O2 14.00% LTS: nematic >1000 h CPY-3-O2 12.00% at −30° C. LTS: nematic >600 h at −40° C.

Example M17

CY-3-O4 16.00% Clearing point [° C.]: 68.5 CY-5-O2 8.00% Δn [589 nm, 20° C.]: 0.1515 BCH-32 8.00% ε_(∥) [kHz, 20° C.]: 4.2 CC-3-V1 10.00% Δε [kHz, 20° C.]: −4.0 CPY-2-O2 12.00% K₁ [20° C.]: 13.0 CPY-3-O2 12.00% K₃ [20° C.]: 14.4 PYP-2-3 11.00% γ₁ [mPa · s, 20° C.]: 161 PYP-3-3 10.00% V₀ [V]: 2.01 B-11FF 13.00% LTS: nematic >1000 h at −40° C.

Example M18

CC-5-V 7.00% Clearing point [° C.]: 70.0 CCH-34 6.00% Δn [589 nm, 20° C.]: 0.0796 CY-3-O4 22.00% ε_(∥) [kHz, 20° C.]: 4.0 CY-5-O4 21.00% Δε [kHz, 20° C.]: −4.8 CCY-2-O2 8.00% K₁ [20° C.]: 12.9 CCY-3-O2 6.00% K₃ [20° C.]: 12.6 CCY-5-O2 7.00% γ₁ [mPa · s, 20° C.]: 172 CCY-2-1 10.00% V₀ [V]: 1.72 CCY-3-1 8.00% LTS: nematic >1000 h CH-33 2.00% at −40° C. CH-43 3.00%

Example M19

CC-5-V 13.00% Clearing point [° C.]: 73.0 CY-3-O4 20.00% Δn [589 nm, 20° C.]: 0.0830 CY-5-O4 20.00% ε_(∥) [kHz, 20° C.]: 3.9 CCY-2-O2 8.00% Δε [kHz, 20° C.]: −5.1 CCY-3-O2 11.00% K₁ [20° C.]: 13.2 CCY-5-O2 8.00% K₃ [20° C.]: 14.0 CCY-2-1 10.00% γ₁ [mPa · s, 20° C.]: 184 CCY-3-1 10.00% V₀ [V]: 1.76 LTS: nematic >1000 h at −20° C. LTS: nematic >800 h at −30° C.

Example M20

PCH-53 5.00% Clearing point [° C.]: 70.5 CY-3-O4 22.00% Δn [589 nm, 20° C.]: 0.0951 CY-5-O4 20.00% ε_(∥) [kHz, 20° C.]: 4.1 CCY-2-O2 9.00% Δε [kHz, 20° C.]: −4.9 CCY-3-O2 10.00% K₁ [20° C.]: 12.9 CCY-5-O2 5.00% K₃ [20° C.]: 13.2 CCY-2-1 12.00% γ₁ [mPa · s, 20° C.]: 210 CCY-3-1 8.00% V₀ [V]: 1.73 BCH-32 4.00% LTS: nematic >1000 h BCH-52 4.00% at −40° C. PGIGI-3-F 1.00%

Example M21

CY-3-O4 16.00% Clearing point [° C.]: 70.0 CY-5-O2 16.00% Δn [589 nm, 20° C.]: 0.1019 CY-5-O4 13.00% ε_(∥) [kHz, 20° C.]: 4.0 CCY-3-O2 9.00% Δε [kHz, 20° C.]: −5.0 CPY-2-O2 12.00% K₁ [20° C.]: 13.8 CPY-3-O2 12.00% K₃ [20° C.]: 14.5 CC-3-V1 10.00% γ₁ [mPa · s, 20° C.]: 165 CCH-35 9.00% V₀ [V]: 1.79 BCH-32 3.00%

Example M22

CCY-3-O2 15.00% Clearing point [° C.]: 87.0 CCY-5-O2 12.00% Δn [589 nm, 20° C.]: 0.0797 CCY-2-1 6.00% ε_(∥) [kHz, 20° C.]: 3.2 CCY-3-1 13.00% Δε [kHz, 20° C.]: −3.1 CY-5-O2 17.00% K₁ [20° C.]: 17.0 CCH-301 7.00% K₃ [20° C.]: 17.8 CCH-35 20.00% γ₁ [mPa · s, 20° C.]: 147 PCH-53 10.00% V₀ [V]: 2.53

Example M23

BCH-32F 2.50% Clearing point [° C.]: 92.0 CCH-301 16.50% Δn [589 nm, 20° C.]: 0.0827 CCH-34 5.00% ε_(∥) [kHz, 20° C.]: 3.4 CCH-35 5.00% Δε [kHz, 20° C.]: −3.0 CCY-2-1 14.00% K₁ [20° C.]: 16.4 CCY-3-O2 13.50% K₃ [20° C.]: 17.8 CCY-3-1 14.00% γ₁ [mPa · s, 20° C.]: 154 CCY-5-O2 13.50% V₀ [V]: 2.58 PCH-301 8.50% CY-3-O2 7.50%

Example M24

CY-3-O4 8.00% Clearing point [° C.]: 91.0 CY-5-O2 3.00% Δn [589 nm, 20° C.]: 0.0822 CCY-3-O2 11.00% ε_(∥) [kHz, 20° C.]: 3.3 CCY-3-O3 12.00% Δε [kHz, 20° C.]: −3.2 CCY-4-O2 12.00% K₁ [20° C.]: 15.4 CPY-2-O2 10.00% K₃ [20° C.]: 15.9 CC-4-V 17.00% γ₁ [mPa · s, 20° C.]: 117 CC-3-V1 12.00% V₀ [V]: 2.36 CCH-35 4.00% LTS: nematic >1000 h CCH-301 11.00% at −20° C.

Example M25

CY-3-O4 12.00% Clearing point [° C.]: 90.0 CCY-3-O3 12.00% Δn [589 nm, 20° C.]: 0.1019 CCY-4-O2 2.00% ε_(∥) [kHz, 20° C.]: 3.4 CPY-2-O2 12.00% Δε [kHz, 20° C.]: −3.0 CPY-3-O2 12.00% K₁ [20° C.]: 15.2 CCH-301 11.00% K₃ [20° C.]: 15.8 CC-5-V 20.00% γ₁ [mPa · s, 20° C.]: 135 CC-3-V1 10.00% V₀ [V]: 2.43 PYP-2-3 2.00% PYP-2-4 4.00% CCPC-33 3.00%

Example M26

CY-3-O4 15.00% Clearing point [° C.]: 90.5 CY-5-O4 11.00% Δn [589 nm, 20° C.]: 0.1249 CY-5-O2 5.00% ε_(∥) [kHz, 20° C.]: 3.7 CPY-2-O2 12.00% Δε [kHz, 20° C.]: −3.3 CPY-3-O2 12.00% K₁ [20° C.]: 15.2 BCH-32 8.00% K₃ [20° C.]: 15.6 PGIGI-3-F 8.00% γ₁ [mPa · s, 20° C.]: 188 CCP-V-1 8.00% V₀ [V]: 2.38 CCP-V2-1 8.00% LTS: nematic >1000 h CC-5-V 9.00% at −30° C. CC-3-V1 2.00% HR (100° C.): 94% CBC-33 2.00%

Example M27

CY-3-O2 12.00% Clearing point [° C.]: 91.0 CY-5-O2 11.00% Δn [589 nm, 20° C.]: 0.0829 CCY-3-O2 14.00% ε_(||) [kHz, 20° C.]: 3.6 CCY-5-O2 15.00% Δε [kHz, 20° C.]: −4.2 CCY-2-1 10.00% K₁ [20° C.]: 16.6 CCY-3-1 14.00% K₃ [20° C.]: 18.4 CCH-34 6.00% γ₁ [mPa · s, 20° C.]: 185 CCH-35 5.00% CCH-301 4.00% CCH-303 5.00% CCH-501 4.00%

Example M28

CY-3-O2 20.00% Clearing point [° C.]: 91.0 CY-5-O2 5.00% Δn [589 nm, 20° C.]: 0.0821 CCY-3-O2 12.00% ε_(||) [kHz, 20° C.]: 3.5 CCY-5-O2 7.00% Δε [kHz, 20° C.]: −4.1 CCY-3-O3 12.00% K₁ [20° C.]: 16.2 CCY-4-O2 11.00% K₃ [20° C.]: 18.1 CC-5-V 20.00% γ₁ [mPa · s, 20° C.]: 148 CC-3-V1 9.00% V₀ [V]: 2.21 CCH-35 4.00% LTS: nematic >1000 h at −20° C.

Example M29

CY-5-O2 9.00% Clearing point [° C.]: 90.5 CY-5-O4 15.00% Δn [589 nm, 20° C.]: 0.1023 CCY-3-O3 12.00% ε_(||) [kHz, 20° C.]: 3.5 CCY-4-O2 10.00% Δε [kHz, 20° C.]: −4.1 CCY-5-O2 10.00% K₁ [20° C.]: 17.3 CPY-2-O2 2.00% K₃ [20° C.]: 16.4 CPY-3-O2 12.00% γ₁ [mPa · s, 20° C.]: 211 CCH-35 7.00% V₀ [V]: 2.10 CCH-303 4.00% LTS: nematic >1000 h at PCH-53 12.00% −20° C. BCH-32 7.00% HR (100° C.): 91%

Example M30

CY-3-O4 5.00% Clearing point [° C.]: 91.5 CY-5-O4 20.00% Δn [589 nm, 20° C.]: 0.1015 CCY-3-O3 12.00% ε_(||) [kHz, 20° C.]: 3.5 CCY-4-O2 10.00% Δε [kHz, 20° C.]: −4.2 CCY-5-O2 11.00% K₁ [20° C.]: 16.6 CPY-3-O2 10.00% K₃ [20° C.]: 16.3 PYP-2-4 7.00% γ₁ [mPa · s, 20° C.]: 211 CC-3-V1 11.00% V₀ [V]: 2.10 CC-5-V 11.00% LTS: nematic >1000 h at PCH-53 3.00% −20° C. HR (100° C.): 94%

Example M31

CY-3-O4 14.00% Clearing point [° C.]: 90.0 CY-5-O2 14.00% Δn [589 nm, 20° C.]: 0.1168 CY-5-O4 4.00% ε_(||) [kHz, 20° C.]: 3.7 CCY-3-O2 6.00% Δε [kHz, 20° C.]: −4.2 CCY-5-O2 7.00% K₁ [20° C.]: 15.3 PGIG1-3-F 2.00% K₃ [20° C.]: 17.7 BCH-32 10.00% γ₁ [mPa · s, 20° C.]: 198 CPY-2-O2 10.00% V₀ [V]: 2.15 CPY-3-O2 14.00% CCP-V-1 2.00% CC-5-V 5.00% CC-3-V1 12.00%

Example M32

CY-3-O4 20.00% Clearing point [° C.]: 87.0 CY-5-O2 12.00% Δn [589 nm, 20° C.]: 0.0808 CY-5-O4 20.00% ε_(||) [kHz, 20° C.]: 3.9 CCY-3-O2 7.00% Δε [kHz, 20° C.]: −5.0 CCY-5-O2 11.00% K₁ [20° C.]: 13.6 CCH-301 5.00% K₃ [20° C.]: 15.1 CH-33 4.00% γ₁ [mPa · s, 20° C.]: 265 CH-35 4.00% V₀ [V]: 1.82 CH-43 4.00% CH-45 4.00% CCPC-33 3.00% CCPC-34 3.00% CCPC-35 3.00%

Example M33

CY-3-O4 14.00% Clearing point [° C.]: 86.0 CY-5-O2 10.00% Δn [589 nm, 20° C.]: 0.1023 CY-5-O4 16.00% ε_(||) [kHz, 20° C.]: 3.9 CCY-2-O2 6.00% Δε [kHz, 20° C.]: −5.1 CCY-3-O2 12.00% K₁ [20° C.]: 15.2 CCY-5-O2 8.00% K₃ [20° C.]: 16.2 CCY-2-1 8.00% γ₁ [mPa · s, 20° C.]: 257 CCY-3-1 12.00% V₀ [V]: 1.89 BCH-32 8.00% LTS: nematic >1000 h at CCP-V-1 4.00% −20° C. PGIGI-3-F 2.00% LTS: nematic >760 h at −30° C. LTS: nematic >500 h at −40° C. HR (20° C.): 98% HR (100° C.): 91%

Example M34

CY-3-O4 10.00% Clearing point [° C.]: 90.0 CY-5-O4 14.00% Δn [589 nm, 20° C.]: 0.1204 CY-5-O2 13.00% ε_(||) [kHz, 20° C.]: 3.9 CCY-3-O2 14.00% Δε [kHz, 20° C.]: −5.0 CCY-5-O2 1.00% K₁ [20° C.]: 14.7 CBC-33 6.00% K₃ [20° C.]: 16.8 CC-5-V 11.00% γ₁ [mPa · s, 20° C.]: 265 PGIGI-3-F 7.00% V₀ [V]: 1.94 CPY-2-O2 12.00% LTS: nematic >1000 h at CPY-3-O2 12.00% −40° C.

Example M35

CY-3-O2 13.00% Clearing point [° C.]: 79.5 CY-5-O2 5.00% Δn [589 nm, 20° C.]: 0.0788 CCY-4-O2 10.00% ε_(||) [kHz, 20° C.]: 3.4 CCY-3-O3 12.00% Δε [kHz, 20° C.]: −3.1 CCY-2-O2V 11.00% K₁ [pN, 20° C.]: 13.9 CPY-2-O2 6.00% K₃ [pN, 20° C.]: 13.6 CCH-303 5.00% γ₁ [mPa · s, 20° C.]: 107 CC-5-V 18.00% V₀ [V]: 2.21 CC-3-V1 12.00% CCH-34 5.00% PCH-301 3.00% 

1. A liquid-crystalline medium based on a mixture of polar compounds having negative dielectric anisotropy (Δ∈), which has a value for the ratio γ₁/Δn² in the range 6-45 Pa·s with a clearing point of >60° C. and a Δ∈ of ≦−2.3, and comprises one or more compounds of formula B-1, B-2 or B-4

at least one compound of formula IB,

and at least one compound of formula II

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms, R¹ and R² each, independently of one another, denote H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, in which one or more CH₂ groups are optionally replaced by —O—, —S—,

 —C≡C—, —OCF₂—, —CF₂O—, —OC—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and v denotes 1 to
 6. 2. A liquid-crystalline medium according to claim 1, which has a clearing point of 60-90° C.
 3. A liquid-crystalline medium according to claim 1, which has a Δ∈ value of −2.3 to −5.5.
 4. A liquid-crystalline medium according to claim 1, which having a clearing point of 70° C.±5° C. and a Δ∈ of −3.0±0.6 has the following rotational viscosities γ₁ at a defined Δn value: Δn γ₁ 0.08 ± 0.005 ≦125 mPa · s 0.09 ± 0.005 ≦130 mPa · s 0.10 ± 0.005 ≦135 mPa · s 0.11 ± 0.005 ≦145 mPa · s 0.12 ± 0.005 ≦150 mPa · s 0.13 ± 0.005 ≦160 mPa · s 0.15 ± 0.01 ≦170 mPa · s.


5. A liquid-crystalline medium according to claim 1, which having a clearing point of 70° C.±5° C. and a Δ∈ of >−3.6 and ≦−4.4 has the following rotational viscosities γ₁ at a defined Δn value: Δn γ₁ 0.08 ± 0.005 ≦140 mPa · s 0.09 ± 0.005 ≦165 mPa · s 0.10 ± 0.005 ≦185 mPa · s 0.11 ± 0.005 ≦190 mPa · s 0.12 ± 0.005 ≦195 mPa · s 0.13 ± 0.005 ≦205 mPa · s 0.15 ± 0.01 ≦220 mPa · s.


6. A liquid-crystalline medium according to claim 1, which having a clearing point of 70° C.±5° C. and a Δ∈ of >−4.4 and ≦−5.6 has the following rotational viscosities γ₁ at a defined Δn value: Δn γ₁ 0.08 ± 0.005 ≦185 mPa · s 0.09 ± 0.005 ≦200 mPa · s 0.10 ± 0.005 ≦210 mPa · s 0.11 ± 0.005 ≦220 mPa · s 0.12 ± 0.005 ≦230 mPa · s 0.13 ± 0.005 ≦250 mPa · s 0.15 ± 0.01 ≦270 mPa · s.


7. A liquid-crystalline medium according to claim 1, which having a clearing point of 90° C.±5° C. and a Δ∈ of −3.0±0.6 has the following rotational viscosities γ₁ at a defined Δn value: Δn γ₁ 0.08 ± 0.005 ≦160 mPa · s 0.09 ± 0.005 ≦170 mPa · s 0.10 ± 0.005 ≦180 mPa · s 0.11 ± 0.005 ≦190 mPa · s 0.12 ± 0.005 ≦200 mPa · s 0.13 ± 0.005 ≦210 mPa · s 0.15 ± 0.01 ≦220 mPa · s.


8. A liquid-crystalline medium according to claim 1, which having a clearing point of 90° C.±5° C. and a Δ∈ of >−3.6 and ≦−4.4 has the following rotational viscosities γ₁ at a defined Δn value: Δn γ₁ 0.08 ± 0.005 ≦185 mPa · s 0.09 ± 0.005 ≦195 mPa · s 0.10 ± 0.005 ≦215 mPa · s 0.11 ± 0.005 ≦215 mPa · s 0.12 ± 0.005 ≦215 mPa · s 0.13 ± 0.005 ≦235 mPa · s 0.15 ± 0.01 ≦250 mPa · s.


9. A liquid-crystalline medium according to claim 1, which having a clearing point of 90° C.±5° C. and a Δ∈ of >−4.4 and ≦−5.6 has the following rotational viscosities γ₁ at a defined Δn value: Δn γ₁ 0.08 ± 0.005 ≦280 mPa · s 0.09 ± 0.005 ≦275 mPa · s 0.10 ± 0.005 ≦275 mPa · s 0.11 ± 0.005 ≦275 mPa · s 0.12 ± 0.005 ≦280 mPa · s.


10. A liquid-crystalline medium according to claim 1, which has thresholds (capacitive) in the range 1.8-2.3 V.
 11. A liquid-crystalline medium according to claim 1, which further comprises a compound of formula IA

in which R¹ denotes H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, in which one or more CH₂ groups are each, independently of one another, optionally replaced by —O—, —S—,

 —C≡C—, —CF₂O—, —CO—, —CO—O—, —O—CO— or —O—CO—O— in such a way that O atoms are not linked directly to one another, and v denotes 1 to
 6. 12. A liquid-crystalline medium according to claim 1, which additionally comprises one or more compounds of the formula III

in which R³¹ and R³² each, independently of one another, denote a straight-chain alkyl, alkylalkoxy or alkoxy radical having up to 12 C atoms, and

denotes

 and Z denotes a single bond, —C₂H₄—, —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CHCH₂CH₂—, —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —CF₂O—, —OCF₂—, —COO—, —OCO—, —C₂F₄—, —CHFCF₂—, —CF═CF—, —CH═CF—, —CF═CH—, or —CH₂—. 13-17. (canceled)
 18. An electro-optical display having active-matrix addressing based on the ECB, PA LCD, FFS or the IPS effect, which contains, as dielectric, a liquid-crystalline medium according to claim
 1. 19. A liquid-crystalline medium according to claim 1, which further comprises in total four compounds of formulae


20. A liquid-crystalline medium according to claim 1, which further comprises at least one compound of formula IIIa and/or IIIb and at least one compound of formula IIIe

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl denotes a straight-chain alkenyl radical having 2-6 C atoms.
 21. A liquid-crystalline medium according to claim 12, which comprises one or more compounds of formulae IIIa to IIIj:

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms.
 22. A liquid-crystalline medium according to claim 12, which comprises one or more compounds of the following formulae


23. A liquid-crystalline medium according to claim 12, which comprises at least three compounds of the following formulae

wherein alkyl denotes C_(n)H_(2n+1), where n=3, 4 or
 5. 24. A liquid-crystalline medium according to claim 1, which comprises a compound of formulae IA and/or IB

in which R¹ is a straight-chain alkenyl or alkyl, and v denotes 1 to
 6. 25. A liquid-crystalline medium according to claim 24, wherein when R¹ denotes alkenyl, said group is CH₂═CH, CH₃—CH═CH, C₃H₇—CH═CH, CH₂═CH—C₂H₄ or CH₃—CH═CH—C₂H₄.
 26. A liquid-crystalline medium according to claim 11, which comprises 10-40% by weight of one or more compounds of the formulae IA and IB, and 10-40% by weight of one or more compounds of the formula II.
 27. A liquid-crystalline medium according to claim 1, which further comprises one or more compounds of the following formulae, which compounds when present are each in an amount of at least 5% by weight

in which R¹³-R²⁷ each, independently of one another, denote H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, in which one or more CH₂ groups are optionally replaced by —O—, —S—,

 —C≡C—, —OCF₂—, —CF₂O—, —OC—O— or —O—CO— in such a way that O atoms are not linked directly to one another, z and m each, independently of one another, denote 1-6, R^(E) denotes H, CH₃, C₂H₅ or n-C₃H₇, and x denotes 0, 1, 2 or
 3. 28. A liquid-crystalline medium according to claim 1, which further comprises one or more compounds of the following formulae T-1 to T-22

in which R denotes H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, in which one or more CH₂ groups are optionally replaced by —O—, —S—,

 —C≡C—, —OCF₂—, —CF₂O—, —OC—O— or —O—CO— in such a way that O atoms are not linked directly to one another.
 29. A liquid-crystalline medium according to claim 1, which further comprises one or more compounds of the following formulae B-1 to B-2

in which alkyl and alkyl* each, independently of one another, denote a straight-chain alkyl radical having 1-6 C atoms, and alkenyl and alkenyl* each, independently of one another, denote a straight-chain alkenyl radical having 2-6 C atoms.
 30. A liquid-crystalline medium according to claim 29, which comprises one or more compounds of the following formulae


31. A liquid-crystalline medium according to claim 1, wherein condition A) applies, wherein the liquid-crystalline medium comprises one or more compounds of the following formulae To-1 and To-2

in which R denotes H, an alkyl or alkenyl radical having up to 15 C atoms which is unsubstituted, monosubstituted by CN or CF₃ or at least monosubstituted by halogen, in which one or more CH₂ groups are optionally replaced by —O—, —S—,

 —C≡C—, —OCF₂—, —CF₂O—, —θOC—O— or —O—CO— in such a way that O atoms are not linked directly to one another, and alkyl denotes a straight-chain alkyl radical having 1-6 C atoms.
 32. A liquid-crystalline medium according to claim 1, which further comprises one or more compounds of the following formula

alkyl* denotes a straight-chain alkyl radical having 1-6 C atoms.
 33. A liquid-crystalline medium according to claim 1, which further comprises at least one compound of the formulae


34. A liquid-crystalline medium according to claim 1, wherein condition B) applies, wherein the liquid-crystalline medium comprises one or more compounds of formulae N-1 to N-5

in which R¹ and R² each, independently of one another, denote straight-chain alkyl, straight-chain alkoxy or straight-chain alkenyl, and Z, Z¹ and Z² each, independently of one another, denote —C₂H₄—, —CH═CH—, —(CH₂)₄—, —(CH₂)₃O—, —O(CH₂)₃—, —CH═CHCH₂CH₂—, —CH₂CH₂CH═CH—, —CH₂O—, —OCH₂—, —COO—, —OCO—, —C₂F₄—, —CF═CF—, —CF═CH—, —CH═CF—, —CH₂— or a single bond.
 35. A liquid-crystalline medium according to claim 1, which further comprises one or more compounds of the following formulae

wherein n=1-12.
 36. A liquid-crystalline medium according to claim 1, which further comprises the following compound

wherein alkyl* denotes a straight-chain alkyl radical having 1-6 C atoms.
 37. A liquid-crystalline medium according to claim 1, wherein alkenyl and alkenyl* each, independently of one another, denote vinyl, 1E-alkenyl or 3E-alkenyl.
 38. A liquid-crystalline medium according to claim 1, wherein R¹ and R² denote straight-chain alkyl or straight-chain alkenyl. 